A pneumatic tire which contains a built-in sealant layer prepared by building a layer of butyl rubber-based composition, which contains a polyisobutylene polymer, following which under the conditions of elevated temperature and pressure used to cure the tire, a major portion of the butyl rubber is presented as being both crosslinked and depolymerized to form a tacky material which has puncture sealant properties in U.S. Pat. No. 4,895,610.
U.S. Pat. Nos. 4,228,839, 4,171,237 and 4,140,167 also relate to a sealant layer in a tire formed by depolymerizing and crosslinking a butyl rubber based rubber composition, particularly by irradiation treatment
Historically, other patents relate to tire constructions, sealant compositions and methods wherein a sealant material is encased or encapsulated in between calendered layers. For example, see U.S. Pat. No. 3,048,509 and said U.S. Pat. No. 4,228,839.
Other methods, sealants and tire constructions have been suggested for puncture sealant pneumatic tires which relate to use of fluid puncture coatings in which the puncture sealant flows into the puncture hole. However, it is considered herein that such liquid puncture sealants may flow excessively under heated conditions and thereby may tend to cause the tire to become out of balance. Also, it is considered herein that many times such a liquid sealant coating would not likely be entirely operable or effective over a wide temperature range extending from summer to winter conditions More complicated structures where a liquid sealant material is encased in a vulcanized material are usually expensive to manufacture and can also create balance and suspension problems due to the additional weight required in the tire. Puncture sealing tires have been built wherein a layer of degraded rubber which is tacky or gummy (of low viscosity) is assembled into the unvulcanized tire. This method of construction is usually only reasonably possible when, for example, the degraded layer of rubber is laminated with another non-degraded layer which permits its handling during the tire building procedure. This is because the tacky, sticky nature and lack of strength in degraded rubber make it very difficult to handle alone without additional support and a barrier to keep it from sticking to a tire building machine or curing apparatus. By laminating the degraded rubber layer between two or more non-degraded rubber layers it is capable of retaining its structural integrity during the vulcanization operation wherein high pressures are applied to the tire which would displace the degraded rubber layer from its desired location if not laminated. Such a lamination procedure adds greatly to the cost of building a tire. Thus, such a lamination procedure has not been widely accepted on a commercial basis for building puncture sealing pneumatic tires. There has been a continuing desire for a pneumatic tire having an effective puncture sealing feature and for a simple and practical method of preparing such a tire.
This invention provides a method for building a tire with puncture sealing features by degrading (depolymerizing) a built-in rubber layer (butyl rubber based rubber composition), which is required to contain a dispersion therein of particles of a precured rubber selected from resin-cured butyl rubber and/or sulfur-cured diene-based rubber, after it is built into the tire and during the vulcanization of the tire. Therefore, during the tire building procedure the butyl rubber-based layer (which will be the sealant layer after the tire is cured) can be built into the tire in a manner similar to other rubber layers.
In the description of this invention, the term “phr” is used to designate parts by weight of an ingredient per 100 parts of elastomer unless otherwise indicated. The terms “elastomer” and “rubber” are used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” are used interchangeably unless otherwise indicated.